The big question my lab addresses is that of protein
function: from the recent progress in molecular biology, we
either know or will know the entire genomes of many organisms. Thus, we
will be able to predict all of the proteins in those organisms. So, how
do these proteins function to achieve the desired biological activity?
Many different tools are needed to adequately study this problem, so my
lab is extraordinarily cross-disciplinary, using biophysical as well as
genetic and biochemical approaches. Of course, this problem cannot be
studied in a vacuum--we need to ask and answer these questions in the
context of a specific biological process. We have chosen to study molecular motors.

These motors are small enzymes that play crucial roles in many
different cellular and developmental processes. Motors such as kinesin
and dynein are required for mitosis and transport of many sub-cellular
organelles such as mitochondria and endosomes, as well as mRNA
localization which is used to set up developmental axis. Motors also
play a role in many diseases: recent work shows that impaired transport
can play a direct role in neuronal degenerative diseases such as
Alzheimer’s, and viruses such as herpes (and probably HIV) hijack the
motors to help them get from the cell’s periphery to the nucleus where
they replicate. Thus, motors are pretty important. How do we study
them?

We use a variety of tools. The role of the motor proteins is to
exert force, and “walk” along a polymer track (such as a microtubule or
actin filament), dragging a cargo (e.g. a vesicle or chromosome or mRNA
particle) with them. So, the functions we want to quantify, to clarify
these proteins activity are a) what is the force
that the motors can apply at a given time, and on a given cargo and b)
how well (i.e. how far and how
fast) do they move along the
polymer track at a given time. From a biophysics perspective, we have
developed two sets of complementary techniques to quantify these
functions. To quantify forces, we use an “optical
tweezers” (a “tractor beam”, like in the science-fiction show
Star Trek) to stop individual moving vesicles and measure the forces
that the motors moving them can exert. To quantify motion, we have
developed particle tracking and
analysis software that allows us to determine the position of
the vesicle with a resolution of 8 nm, 30 times a second. So, we can
accurately quantify the important aspects of motor function.

In addition, we work in Drosophila, so we can use genetics
or biochemistry to identify
which proteins play a role in these processes. By making a mutation in a
particular protein, and then using the biophysical tools to quantify how
the motor functions were changed, we can better understand exactly what
role that protein has in the overall process. Finally, by using
biochemistry, we can investigate molecular interactions, to start to
build a molecular picture of the way the motors are regulated. These
more molecular models can then be tested by quantifying motion in a
background with a more specifically engineered mutation, or by use of
small peptides designed to block a particular molecular interaction.
Thus, we integrate biophysics, biochemistry, and genetics to better
understand protein function in vivo and in vitro.

To try to learn general rules,
we study and compare the regulated motion of two different cargos: lipid droplets moving in early
embryos of the fruitfly Drosophila, and pigment
granules moving in a cultured cells derived from the frog
Xenopus laevis.